This invention generally relates to bipolar transistor epitaxial deposition methods and, more particularly, to the selection of pressure during the epitaxial growth process to maximize bipolar device performance and leakage limited yield.
It is known that autodoping of impurity ions occurs in growing epitaxial layers as a result of the incorporation of such ions from so called "buried layer" impurity regions in the substrate upon which the epitaxial layer is grown, and in particular, the arsenic autodoping can be reduced by reduced pressure epitaxial growth as described in U.S. Pat. No. 3,765,960 entitled "Method for Minimizing Autodoping in Epitaxial Deposition" to D. W. Boss et al, Oct. 16, 1973 and assigned to the assignee of the present invention. It is also known that autodoping is a function of the autodoping source area and that boron autodoping, for example, increases with decreasing deposition pressure while arsenic autodoping increases with increasing pressure. This is discussed in the IBM.RTM. Technical Disclosure Bulletin article "Eliminating Boron and Arsenic Autodoping Through Reduced Pressure" by A. K. Gaind et al., Vol. 24, No. 3, August 1981, page 1731, which reports the results of autodoping experiments in which various numbers of blanket boron or arsenic-diffused test wafers were placed in a reduced pressure epitaxial deposition reactor.
Although it has been surmised that an optimum epitaxial deposition pressure is required for each wafer configuration to reduce lateral autodoping, the heretofore unknown interrelationship of deposition pressure with the other parameters of device wafer processing has made autodoping minimization an elusive goal.